1. Field of the Invention
This invention has relation to a fork lift truck and more particularly to an apparatus whereby the pay load being picked up, carried and delivered by a fork lift truck, and the mast and carriage supporting the pay load, can be maintained in a substantially upright condition when the truck encounters uneven ground.
2. Description of the Prior Art
Fork lift trucks are well known in industrial, commercial and agricultural environments for use in picking up a pay load (whether or not on a pallet), moving it to a needed location, and depositing it at that location to a desired position. Typically such equipment consists of a wheel supported truck body, a pair of primary load support wheels at a front end portion of that body, an elongate mast supported by the truck body near the support wheels, and a carriage including, typically, a pair of parallel, spaced-apart fork lift tines, the carriage being power operated to move up and down the mast as needed.
Where such trucks are used in a closed industrial location having a substantially flat horizontal floor throughout, the problem of picking, transporting and delivering the pay load is relatively simple. However, it is known in the prior art to provide a straight horizontal mast support bar extending across a front end portion of the truck body and to mount the mast on a sleeve which is supported by the horizontal mast support bar and is movable along it in a horizontal direction. Hydraulic means has been provided to move the sleeve along the bar so that when the truck lift operator brings a pay load into a position where it is to be unloaded, but finds that the pay load, carriage and mast are a few inches out of alignment with the desired final positioning of the pay load, the mast, carriage and pay load can be shifted several inches one way or the other along the mast support bar, until the proper alignment is achieved and deposit or delivery of the pay load can be made.
When working outside over rough terrain, another problem presents itself. The unevenness of the terrain can cause a pay load resting on the forks of a fork lift carriage to assume a position other than horizontal so that it is difficult or impossible to move the pay load into a desired bin opening, for example, without leveling the pay load.
Also, when the fork lift truck must move over uneven ground, there is the problem of keeping the pay load and the fork lift portion of the carriage sufficiently level so that the pay load will not fall from the mast. One solution offered for this problem has been to make the carriage which moves up and down on the mast in two distinct units, one part being movable up and down the mast at whatever angle the mast assumes when the truck is traveling over uneven ground, and a second part of the carriage, including the fork lift tines, being rotatable with respect to the first part of the carriage so that the pay load and the tines can be maintained in a substantially horizontal orientation.
A drawing of a prior art structure commonly used to provide horizontal alignment for a pay load package on a carriage even though the fork lift truck is not on horizontal ground is illustrated in FIG. 5 as part of the prior art. In this figure, a wheel supported fork lift truck 110 is supported on primary load support wheels 114,114 and includes a perfectly straight elongate mast support bar 115 on which a mast 130 is supported. As the fork lift truck moves onto non-horizontal ground such as illustrated at 148, the mast 130 maintains its position normal to the surface on which the support wheels 114,114 rest and takes up the position as seen in FIG. 5. In order to be able to unload a pay load package 150 onto a horizontal surface, this prior art structure provides that a first part of a carriage (not shown) moves in parallel relation to the tilting fork lift mast 130 while the second forward part of the carriage, including fork lift tines 146,146 is rotated with respect to the first part of the carriage to position as seen in FIG. 5.
As clearly seen in that figure, this puts the center of gravity of the pay load package far from the center of gravity of the truck itself, and can move the center of gravity of the load very easily outside of the outer edges of the primary load support wheels 114,114. This can easily lead to a tip over of the lift truck and consequently a dumping of the load. Some idea of the dangers involved in this prior art structure can be gleaned from the ratings of Allis-Chalmers Lift Trucks in their Industrial Truck Buyer's Guide, Document MH-1102A dated April 1985 in which their Model ACP 100C has a weight of only 14,500 pounds and an overall width of 54.6" and is rated to be able to lift 10,000 pounds.
A structure which makes it possible to operate a lift truck on non-horizontal ground and still maintain the center of gravity well within the outside of the support wheels, was clearly needed before the present invention.
Neither the inventor nor those in privity with him are presently aware of any prior art which is closer than that discussed above and are not aware of any prior art which renders unpatentable any of the claims made herein.